Nodular cast iron and process of making same



United States Patent NODULAR CAST IRON AND PROCESS OF MAKING SAME Henton Morrogh, Tanworth-in-Arden, England, assignor, by mesne assignments, to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware No Drawing. Application February 6, 1952 Serial N 0. 270,282

Claims priority, application Great Britain February 7, 1951 12 Claims. (Cl. 75-125) The art of producing an improved hypo-eutectic cast iron by means of the addition of magnesium is now well known. Under appropriate conditions now well understood, magnesium converts the lamellar flake graphite of normal cast iron into a nodular form sometimes referred to as spheroidal or spherulitic graphite, and so gives a cast iron which has much improved properties and which may be ductile. After the addition of the magnesium it is the practice to inoculate the molten metal with a graphitising inoculant such as ferro-solution. It is now well established by the practised art that the magnesium may be added to the molten cast iron in the form, for instance, of a nickel-magnesium-carbon alloy having between 5 and 20% magnesium. It has also been realised that magnesium can be added to cast iron as a copper-magnesium alloy having, for instance, between 5 and 25% magnesium. It has been less well appreciated, however, that copper alloyed with the iron, certainly in amounts in excess of 1%, inhibits the ability of magnesium to give nodular structures. This is an important limitation of the process whereby nodular cast irons are produced by adding magnesium to the molten cast iron, particularly since some cast irons have copper as an integral part of the compositions; for instance, cast irons having about 12-15% nickel, 2% chromium and 67% copper find many applications on account of their resistance to corrosion and heat. Moreover the use of a copper-magnesium alloy for the introduction of magnesium may at the same time raise the copper content of an otherwise suitable iron to beyond 1%.

It is the object of the present invention to providea means whereby the effect of copper in inhibiting the production of nodular graphite structures in magnesiumtreated irons containing copper may be eliminated, and to provide a means whereby nodular irons containing more than 1% of copper can be produced.

The invention involves the addition of cerium prior to, simultaneously with or after the addition of magnesium, but preferably simultaneously with the magnesium. After treatment and solidification the iron may contain 0.001% to 0.20% cerium and 0.02%-0.20% magnesium but in general the iron will have 0.01% to 0.02% cerium and 0.04% to 0.06% magnesium. The final copper content of the solidified casting may have any value up to 7% and may be present as an alloying element in the iron before treatment, or may arise wholly or in part from the addition of the magnesium as a copper-magnesium or a copper-magnesium-cerium alloy. The magnesium may be added by any convenient method and the cerium may be added as any alloy or as mischmetall, or any alloy with mischmetall.

Provided the iron will solidify grey the composition may vary between wide limits as indicated below:

Carbon Up to 4.3 /s(% Si+P) Silicon Up to 7%.

Manganese Up to 7%.

Phosphorus Up to 2% preferably below 0.1%. Sulphur Before treatment up to 0.25%.

"ice

The elements nickel, chromium and molybdenum may also be present either singly or in any combination provided the iron will solidify grey.

Whilst the sulphur content of the untreated metal can have any value up to 0.25% it is good practice to keep this value as low as possible. In general the sulphur content of the treated metal will be somewhat reduced by the magnesium addition but it will not .necessarily be reduced to such a low value as would be achieved if the magnesium was added without the cerium. For instance, with an iron having initially 0.1% sulphur treated according to this invention the final sulphur content might assume a value of 0.035%, whereas with magnesium unaccompanied by cerium it would have to be reduced to about 0.015% before a nodular structure would be produced.

The invention is illustrated but not limited by the following examples. 0

was melted and the melt divided into two portions. One portion was treated with a nickel-magnesium alloy and then inoculated with ferro-silicon. The other portion was treated with a nickel-magnesium-cerium alloy and similarly inoculated.

A test bar cast from the first portion was found to contain 0.065% magnesium and had a tensile strength of 14.1 tons/sq. in. A test bar cast from the second portion contained 0.062% magnesium and had a tensile strength of 22.6 tons/ sq. in.

Example 11 An iron of the following composition:

Percent Total carbon 3.34 Silicon 1.86 Manganese 0.48 Sulphur 0.123 Phosphorus 0.05

was melted and divided into two portions, which Were treated, respectively, (a) with 2.5% of a copper-magnesium alloy (15% magnesium), and (b) with 2.5% of a copper-magnesium-cerium alloy (14.2% magnesium, 2.2% cerium), each being then inoculated with ferrosilicon silicon). Test bars cast from the two portions gave the following results.

Mg. Cu, Ce, Tensile Test perperper- Strength, Mlerostructure Bar cent cent; cent Tons/sq.

a 0.065 2.1 13.0 Flake graphite ina matrix of pearlite. b 0.053 2.03 0.010 43.7 Graphite nodules ina matrix of pearlite.

I claim: 1. Process for the production of grey cast iron which contains copper, is hypoeutectic in relation to carbon, and in which the graphite is present at least predominantly in the form of nodules, which process comprises adding magnesium and cerium to a molten iron which contains copper, is hypoeutectic in relation to carbon. and which on casting gives a grey cast iron, and casting the treated melt; the treated melt having a copper content of about 2% to. 7% which would substantially interfere with the nodularizing action of the magnesium in the absence of cerium.

2; Process as claimed in claim 1 in which the cerium is added before the magnesium.

3'. Process as claimed in claim 1 in which the cerium is added. after the magnesium.

4. Process as claimed in claim 1 in which the magnesium and. the cerium are added together in the form ofan alloy containing both metals.

5. Process as claimed in claim 1 in which the magnesium and the cerium are. added together in the form of an alloy containing both these metals and a metal selected from the group consisting of nickel and copper.

6. Process as claimed in claim 1 in which the amounts of magnesium and cerium added are such that the iron after casting contains at least 0.001% and at most 0.20% of cerium, and at least 0.02% and at most 0.20% of magnesium.

7. Process. as. claimed in claim 1 in which the copper content of the iron after casting is at least 1% and at most 7%.

8. Process as claimed in claim 1 in which after the addition of magnesium and cerium and immediately before casting there is added an inoculant.

9. Process as claimed in claim 1 in which, after the addition. of magnesium and cerium and immediately before casting there is added as inoculant ferrosilicon.

10. Grey cast iron, hypoeutectic in relation to carbon, and containing copper, magnesium and cerium, the graphite in the said cast iron being at least predominantly in the form of nodules, the content of magnesium and cerium taken together not exceeding about 0.40%, and the copper content being about 2% to 7%.

11. Grey cast ironv asclaimed in, claim 10, in which the copper, magnesium and cerium are present in the following proportions: copper from 2 to 7%; magnesium from 0.02 to 0.20%; cerium from 0.001 to 0.20%.

12. Grey cast iron as claimed in claim 10, in which the copper, magnesium; and cerium are present in the following proportions: copper from 2 to 7%; magnesium from 0.04 to 0.06%; cerium from 0.01 to 0.02%.

References Cited in the file of this patent UNITED STATES. PATENTS 2,542,655 Gagnebin et a1. Feb. 20, 1951 2,603,563 Creme July 15, 1952 2,622,022 Crome Dec. 16, 1952 FOREIGN PATENTS 1,035,055 France Apr. 15,. 1953 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,841,489 July 1, 1958 Henton Morrogh It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and t Patent should read as corrected below.

Column 1, line 24, for "ferro solution" read ferro silicon Signed and sealed this 4th day of November 1958.

Attest:

KARL H. AXLINE Attesting Officer ROBERT C. WATSON Commissioner of Patent hat the said Letters 

1. PROCESS FOR THE PRODUCTION OF GREY CAST IRON WHICH CONTAINS COPPER, IS HYPOEUTECTIC IN RELATION TO CARBON, AND IN WHICH THE GRAPHITE IS PRESENT AT LEAST PREDOMINANTLY IN THE FORM OF NODULES, WHICH PROCESS COMPRISES ADDING MAGNESIUM AND CERIUM TO MOLTEN IRON WHICH CONTAINS COPPER, IS HYPOEUTECTIC IN RELATION TO CARBON AND WHICH ON CASTING GIVES A GRAY CAST IRON, AND CASTING THE TREATED MELT; THE TREATED MELT HAVING A COPPER CONTENT OF ABOUT 2% TO 7% WHICH WOULD SUBSTANTIALLY INTERFERE WITH THE NODULARIZING ACTION OF THE MAGNESIUM IN THE ABSENCE OF CERIUM. 